β-Cyclodextrin at the Water/1-Bromobutane Interface: Molecular Insight into Reverse Phase Transfer Catalysis

Abstract

Molecular insight into the role of β-cyclodextrin (βCD) as a phase transfer catalyst at the liquid/liquid interface is obtained by molecular dynamics simulations of the structure and dynamics of βCD adsorbed at the interface between water and 1-bromobutane. In particular, we consider the structure and dynamics of the water and bromobutane molecules inside the βCD cavity and compare them with the behavior when βCD is dissolved in bulk water. βCD is preferentially oriented at the interface, with the cavity opening along the interface normal. While in bulk water the cavity includes 6-8 water molecules that are relatively mobile with short residence time, at the interface the cavity is mostly dehydrated and includes a single bromobutane molecule. This inclusion complex is stable in bulk water. The implication of this behavior for reverse phase transfer catalysis is discussed.

Structure and Dynamics of Host/Guest Complexation at the Liquid/Liquid Interface: Implications for Inverse Phase Transfer Catalysis

“…The population distribution is approximately Gaussian in shape, with a maximum at nine water molecules in the pore. This peak is slightly higher than our previously reported value and can be attributed to the less restrictive definition of the β-CD pore as a cylinder versus the spherical definition used in the earlier work. Figure b shows the pore populations of selected 1-bromooctane moieties in bulk 1-bromooctane.…”

“…The orientation of 1-bromooctane molecules as a function of position on the z axis is a useful parameter to consider when investigating the role of β-CD in IPTC. It has been reported by several groups that the β-CD molecule orients its cavity openings parallel to the interface when at the liquid/liquid interface and exhibits random orientation in the bulk. , The combination of these results suggests a few mechanistic possibilities regarding the IPTC utility of β-CD. The orientation of a β-CD/1-bromooctane host/guest complex at the interface can orient the reactive group toward the aqueous nucleophilic reactants.…”

“…The purpose of the present work is to investigate the β-CD/1-bromooctane/water system using molecular dynamics simulations and obtain molecular insight into the IPTC mechanism. We recently reported molecular dynamics simulation results that surveyed a system similar to that used in the Triponov–Nikiforov experiments: β-CD at the water/1-bromobutane interface . In our simulations, the β-CD molecule was found to be quite surface-active, with its center of mass rarely being more than 10 Å from the Gibbs dividing surface (GDS).…”

Reactions and Polymerizations at the Liquid–Liquid Interface

“…In IPTC, similar to PTC, a lipophilic substrate is transferred into the aqueous phase by the catalyst and the reaction takes place in the aqueous phase. Pyridine derivatives such as DMAP are popular catalysts due to their low cost but also cyclodextrins, , calixarenes, and, as shown in the following example, surfactants are applicable.…”

Copper‐supported β‐cyclodextrin‐functionalized magnetic nanoparticles: Efficient multifunctional catalyst for one‐pot ‘green’ synthesis of 1,2,3‐triazolylquinazolinone derivatives

“…Copper is an active catalyst and therefore has found numerous applications in several organic transformations . β‐Cyclodextrin (BCD) is a seven‐membered sugar ring molecule and is used as phase transfer and interface reaction catalyst, and it can include water‐insoluble organic materials in its cavity in aqueous solution . In addition, BCD has been shown to be an appropriate ligand for copper for application in 1,3‐dipolar cycloaddition …”